INTERNAL EAE. 



529 



which is continuous, through the Eustachian tube, with that of 

 the guttural pouch and pharynx, and is reflected into the mastoid 

 cells. The whole of this membrane is lined with epithelium, 

 that in the tube being ciliated. 



INTERNAL EAR. 



The internal ear, from its complexity termed the labyrinth, is 

 the ultimate part of the organ of hearing. It consists of a cavity 

 whose boundaries include 

 an osseous outer, and a 

 membranous inner por- 

 tion, respectively termed 

 the hony and the mem- 

 branous labyrinths. 

 The bony labyrinth is an 

 irregular cavity, divided 

 into three separate parts; 

 the vestibule, semicircu- 

 lar canals, and cochlea. 



The Vestibule is an 

 irregular, oval - shaped 

 cavity, situated between 

 the cochlea and the semi- 

 circular canals, having 

 the fenestra ovalis pene- 

 trating its outer wall, 

 and the five round open- 

 ings of the semicircular 

 canals at its back. At 

 the upper part of its 

 inner wall are two de- 

 pressions, the fovea 

 elliptica and fovea 

 hemispherica, separated 

 by a ridge, the emi- 

 nentia pyramidalis, all 

 of which are pierced by 

 numerous small open- 

 ings, macula cribrosa, for the passage of nerve filaments. • Behind 

 the fovea hemispherica is the opening of the aqueduct of the 



2 M 



Diagram of the ear. 



In the internal portion, the black 

 part shows the cavities of the bony, and the white part those 

 of the membranous labyrinth. Ovi, Cavity of the concha ; 

 aG, External auditory meatus; Tr, Tympanic membrane ; 

 Ct, Tympanum ; Ak, Auditory ossicles ;. Fr, Fenestra 

 rotunda ; ER, Eustachian tube ; L, Guttural pouch ; Sac, 

 Sacculus ; ut, Utricle ; oB, uB, Bony ; Co, hB, Membranous 

 semicircular canals ; De, Aquasductus vsstibuli ; Se, Saccus 

 endolymphaticus ; St, Scala tympani ; Sv, Scala vestibuli ; 

 Con, Scala intermedia ; +, Its vestibular caecal sac ; Cr, 

 Ductus reuniens ; *, Its apex : Dp, Aquaeductus cochleae, 

 vel Cotunnii. 



